- Slides: 27
Meiosis Chapter 10, Section 2
Meiosis Activity 1. You need one textbook for every two students. 2. You will be taking notes from the screen and using your textbook.
Genes and Chromosomes Punnett squares help us to study a few genetic traits at a time Organisms actually have tens of thousands of genes that make each of us unique Genes are lined up on chromosomes One chromosome can contain a thousand genes along its length
Turn to page 265 in the textbook With your partner, find the bold word: meiosis. Read about meiosis and answer the following questions. Be prepared to share your answers with the class! 1. Does meiosis occur in regular body cells like the liver, heart, and skin cells? 2. Why is it important for organisms to produce cells with HALF the number of chromosomes?
Diploid & Haploid Cells Diploid = a cell with two sets of chromosomes, 2 n Haploid = a cell with one set of chromosomes, gametes, 1 n Meiosis forms haploid gametes required for sexual reproduction Meiosis has 2 stages – Meiosis II
Turn to page 265 Study Table 10. 1 Chromosome Numbers of Common Organisms and answer the following questions with your partner. Be prepared to share your answers. 3. What does the ‘n’ stand for in the table? 4. Look at the data for the leopard frog. Why is the number in the body cell column double the number in the gamete column?
MEIOSIS I Separation of homologous pairs Homologous Pair = in a diploid cell the 2 sets of chromosomes pair up
1. Prophase I DNA coils into chromosomes Nuclear envelope & nucleolus break down Synapsis = homologous chromosomes pair up into tetrads Crossing-over = homologous pairs switch pieces of their chromatids Genetic Recombination = maternal & paternal genetic info get shuffled during crossing-over
Turn to page 269 Study Figure 10. 13 and answer the following questions. Be prepared to share your answers! 5. Are sister chromatids identical or different to each other? What about homologous pairs? 6. In part C, if you put the four chromosomes back into pairs, would they be the same as the original Homologous chromosomes in part A?
2. Metaphase I Tetrads line up in the middle of the cell Spindle fibers attach at the centromeres of each homologous chromosome
Homologous chromosomes line up side by side as tetrads
3. Anaphase I Each homologous chromosome moves to the opposite end of the cell Independent Assortment = random separation of chromosomes, allows for genetic variation
4. Telophase I & Cytokinesis I Two newly formed cells are haploid Each chromosome is still made up of two chromatids
Humans have 46 chromosomes (23 pairs) 7. With your partner, discuss what would happen if the formation of gametes stopped after meiosis I. How many chromosomes would the resulting human end up with? Be prepared to share with the class!
MEIOSIS II Separation of sister chromatids Sister Chromatids = identical halves of a chromosome that has been duplicated
5. Prophase II 2 newly created cells from Meiosis I start to divide
6. Metaphase II Chromosomes line up in the center
7. Anaphase II Sister Chromatids separate
8. Telophase II & Cytokinesis II 4 new cells, each with half the number of chromosomes of the original cell
Development of Gametes Spermatogenesis = production of sperm cells Oogenesis = production of mature egg cells
Pictures on pg 267!!!
Turn to page 269 Read the section titled Meiosis Provides for Genetic Variation and answer the following questions: 8. Describe the major difference between cells formed by mitosis and cells formed by meiosis. 9. What is “variability” and why is it important to us?
Nondisjunction = failure of homologous pairs to separate in Meiosis I If an organism survives, it may have a genetic disorder
Polyploidy Polyploid = organisms with more than the usual number of chromosome sets Occurs frequently in plants, results in plants that are larger than normal